A power train system for a hybrid vehicle includes, as illustrated in FIG. 1, an engine 10 and a motor 12 serially arranged with each other. An engine clutch 13 is arranged between the engine 10 and the motor 12 to transmit or block power from the engine. An automatic transmission 14 is provided for shifting and outputting power from the motor and the engine to the wheels. A hybrid starter generator (HSG) 16, which is a kind of motor, is connected with a crank pulley of the engine so that power is transmittable to generate power for starting the engine and charging the battery. An inverter 18 is provided for controlling the motor and controlling power generation, and a high voltage battery 20 is connected with the inverter so as to be chargeable/dischargeable, so that power is provided to the motor 12 and the like.
The power train system for the hybrid vehicle is a type in which the motor is attached to the automatic transmission, and is called a transmission mounted electric device (TMED) scheme. It provides travelling modes including an electric vehicle (EV) mode that is a pure electric vehicle mode using only the power of the motor, a hybrid electric vehicle (HEV) mode using the power of the engine as the main power and the power of the motor as auxiliary power, and a regenerative braking (RB) mode, in which the motor collects braking and inertia energy of the vehicle through power generation and charges the battery while the vehicle brakes or travels by inertia.
In a hybrid vehicle using electric power from both the engine and the driving motor, the engine is generally operated in a region having high efficiency, and the remaining power is charged or discharged by the motor.
To this end, an air-fuel ratio is generally controlled so that the engine lambda is 1.
However, in the related art, when the hybrid vehicle including the engine and the driving motor travels, the power of the engine and/or the driving motor is distributed within a range of physically outputtable maximum torque of the engine and maximum available torque of the driving motor, so that travelling performance in a situation requiring high torque, where the torque required by the driver is high, is not provided.
Accordingly, even though fuel efficiency deteriorates in a situation requiring high torque, because of continuous use of the accelerator by the driver, it is necessary to perform an operation where the engine lambda<1 (an operation in which a large amount of fuel is injected), in order to increase engine output to provide the torque required by the driver.
In a situation where a state of charging (SOC) of the battery is low, it is necessary to charge the battery by increasing the output of the engine, which is a power source for charging the battery even though the situation where engine lambda=1 is not maintained.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.